Wheel alignment in a vehicle, expressed for example as toe-in and camber angle, is an important factor affecting the straight-line stability and steering characteristics of the vehicle, and in vehicle adjustment and inspection there is a need for its precise measurement.
A factor influencing the measurement of wheel alignment is sideways runout of the wheel, which arises from the state of the mounting of the wheel to the vehicle. When there is runout of the wheel, measured wheel alignment values deviate by an amount corresponding to the wheel runout.
Technology for obtaining wheel alignment while taking into account the affect of this runout is disclosed for example in Japanese Patent Publication No. HEI-4-5934, “WHEEL INSPECTION SYSTEM FOR 4-WHEEL VEHICLE”.
This vehicle inspection system has a support table fitted with a spaced left-right pair of contact roller assemblies. The left contact roller assembly has two rotatable contact rollers. The right contact roller assembly also has two rotatable contact rollers. The left pair of contact rollers press on one side face of a vehicle wheel, and the right pair of contact rollers press on the other side face of the wheel. An angle sensor for detecting an angle of turn of the support table, that is, a runout angle corresponding to the runout of the wheel, is provided on the underside of the support table.
However, in this vehicle inspection system, for example, during runout measurement, it sometimes happens that an external force acts on the wheel, and under this external force the wheel is forcibly shifted and the measured runout value is affected.
FIG. 14 is a graph illustrating the affect of shifting of the wheel during wheel runout measurement in related art. The vertical axis shows wheel runout Sv and the horizontal axis shows time t. When rotation of the wheel is started, the wheel runout Sv varies sinusoidally with time. A predetermined time from the start of rotation of the wheel is spent running in, and after this running-in a measurement period during which the wheel turns through one revolution is provided for measuring runout.
If during this measurement period the wheel axle shifts due to a change in the weight of the vehicle under test or a movement of its steering wheel and the wheel runout Sv changes by for example δ, when the difference D1 between the maximum and minimum values of the wheel runout in the measurement period is then measured as the wheel runout amplitude, the wheel runout amplitude D2 which is actually being sought will not be measured, and an accurate wheel runout amplitude will not be obtained. As a result, it is difficult to measure aspects of wheel alignment such as toe-in and camber angle accurately.